Imaging of Presumed Displaced Retinal Ganglion Cells in the Living Human Retina

Abstract

Purpose : Large somas hypothesized to be displaced retinal ganglion cells (dRGCs) have previously been reported by our group at the inner edge of the inner nuclear layer (INL) of human subjects with adaptive optics optical coherence tomography (AO-OCT). dRGCs have been studied in numerous mammals but have not yet been classified in the human retina. To characterize this cell population, a prospective pilot study was performed obtaining AO-OCT images of the INL in human subjects.

Methods : The right eye from five healthy subjects aged 26.6 ± 1.3 years was imaged. Subjects with retinal pathology or high refractive error were excluded. The Indiana AO-OCT system was utilized to obtain 1.5°×1.2° volume images at 8 locations: 2°, 3°, 6°, 8°, and 13° temporal and 2°, 3°, and 6° nasal to the fovea, along the horizontal meridian of the retina. ImageJ™ software was used to manually view, count, and measure the en-face area of all large somas at the INL edge. Morphometric biomarkers of soma density, diameter and spatial distribution were measured. Also, AO-OCT images of subjects with glaucomatous arcuate defects were reviewed to assess dRGC presence in the defect.

Results : dRGC soma density was greatest near the fovea and decreased monotonically with increasing retinal eccentricity in all subjects (maximum average of 543.4 cells/mm² at 2° nasal; minimum average of 38.0 at 13° temporal). See Fig. 1. This trend is consistent with that of retinal ganglion cells (RGC), except near the fovea where RGC density peaks parafoveally^1,2 and dRGC density continues to increase as close as 2° from the fovea. Soma size and its standard deviation increased monotonically with increasing retinal eccentricity, from 13.0 ± 1.4 mm at 2° temporal to 16.0 ± 1.5 mm at 13° temporal. Size and size variation are consistent with that of ganglion cell layer somas at the same retinal eccentricities as reported in the literature (11.4 ± 1.8 mm at 1.5-3° and 13.9 ± 3.1 mm at 12–13.5°).¹ All glaucoma images showed reduced numbers of dRGCs in the area of the arcuate defect compared to healthy individuals.

Conclusions : We obtained the first morphometric measurements of presumed displaced RGCs in the INL of the living human retina.

1. Liu, et al. PNAS. 2017;114(48):12803-8
2. Curcio, Allen. J. Comp. Neurol. 1990;300:5-25

This is a 2021 ARVO Annual Meeting abstract.

 

Fig. 1: Comparison of dRGC and RGC density with retinal eccentricity

 

Fig. 2: AO-OCT image of dRGC somas at 6° temporal to the fovea